1. Field of the Invention
The invention relates to a collecting pit for receiving molten metal and cooling water upon the occurrence of failures in metal melting arrangements or metal holding arrangements, which collecting pit is equipped with a drainage layer formed of slag granulate, in particular cupola slag granulate, in which a plurality of small channels is provided in a pore-like distribution, through which water getting on the drainage layer runs off to an outlet, while molten metal is held back by the drainage layer.
2. Description of Relevant Art
Collecting pits of the above-mentioned type are known, in which the drainage layer is comprised of loosely filled-up fine grained slag, in particular, cupola slag, and this slag is destined to allow water getting on the drainage layer to flow off, while molten metal, in particular molten iron, is held back by this drainage layer, which causes sintering of the slag on the surface of contact within the metal. However, due to the rough ambient conditions prevailing in metal melting plants, the water permeability of such a drainage layer comprised of loosely filled-up slag is largely deteriorated after some time. In the region of such collecting pits, vibrations and shocks occur frequently, involving redensification of the filled-up slag material, thus causing the channels formed between larger slag grains to be obstructed by fine material contained in the slag, and additional fine material is formed from larger slag grains also by shocks and vibrations, accelerating and intensifying the obstruction of the channels required for water drainage. In this manner, the drainage of water through the drainage layer is strongly impeded since the water, instead of running through channels between larger slag grains, only tends to trickle through the pores of the slag materials. This not only has the disadvantage of water passing the drainage layer relatively slowly, but also has the disadvantage of relatively large amounts of water being stored in the drainage layer, such stored water leaving the drainage layer very slowly. The obstruction of the channels initially provided in the drainage layer between larger slag grains by fine material and the redensification of the slag material are still intensified in an adverse way by water frequently getting into such collecting pits in many fields of operation and plants such that the reduction of water permeability of the drainage layer occurs after a relatively short period of time. Such a decrease of the permeability of the drainage layer, like the increase in the amount of water stored in the drainage layer, considerably affects the safety function of such a collecting pit, since water present in the drainage layer may lead to explosion-like occurrences due to the formation of vapor as molten metal reaches the drainage layer.
Replacement of such a drainage layer provided in known collecting pits after its water permeability has deteriorated is complex and cumbersome, because the drainage layer provided in the bottom region of the collecting pit is covered by covering elements on which partition walls are mounted as a rule, the partitions subdividing the collecting pit into individual compartments.